The invention relates to holographic data storage media, and more particularly to substrates capable of containing a viscous holographic recording material during media fabrication.
Many different types of data storage media have been developed to store information. Traditional media, for instance, include magnetic media, optical media, and mechanical media to name a few. Increasing data storage density is a paramount goal in the development of new or improved types of data storage media.
In traditional media, individual bits of information are stored as distinct mechanical, optical, or magnetic changes on the surface of the media. For this reason, data storage medium surface area imposes physical limits on data densities for a given recording technique.
Holographic data storage media can offer higher storage densities than traditional media. In a holographic medium, data can be stored throughout the volume of a holographic recording material. In other words, holographic media permit three-dimensional data storage. Theoretical holographic storage densities can approach tens of terabits per cubic centimeter.
In holographic data storage media, entire pages of information, e.g., bitmaps, can be stored as optical interference patterns within a photosensitive holographic recording material. The optical interference patterns can be generated by intersecting two coherent laser beams within the recording material. The first laser beam, called the object beam, contains the information to be stored; and the second laser beam, called the reference beam, interferes with the object beam to create an interference pattern that can be stored in the recording material as a hologram. When the stored hologram is later illuminated with only the reference beam, some of the light of the reference beam is diffracted by the holographic interference pattern. Moreover, the diffracted light creates a reconstruction of the original object beam. Thus, by illuminating a recorded hologram with the reference beam, the data encoded in the object beam can be recreated and detected by a data detector such as a camera.
Holographic data storage media may have a sandwiched construction in which a photosensitive holographic recording material, such as a photopolymer formulation, is sandwiched between two substrates and then cured. The holograms are recorded and stored in the holographic recording material. The holographic recording material, however, is typically in a viscous fluid or gel-like form when it is originally sandwiched between the substrates. The viscous nature of the holographic recording material can present challenges in media fabrication.
The invention is directed to holographic data storage media having a sandwiched construction in which a holographic recording material is sandwiched between two substrates. Various substrate features are described that may improve media quality, simplify the manufacturing process, and provide improved environmental stability to the created media.
For example, one or both of the substrates may be formed with fluid containment features in proximity to outer edges of the respective substrates. Also, the substrates may be formed with centerpieces rather than a center hole. The centerpieces may also be recessed relative to outer surfaces of the respective substrates.
In one embodiment, a holographic data storage medium comprises a first substrate, a second substrate, and a holographic recording material between the first and second substrates. At least one of the substrates, and possibly both of the substrates, may be formed to include fluid containment features in proximity to the outer edge(s) of the substrate(s). The fluid containment features may serve to define a cavity between the substrates that can contain a holographic recording material when the material is in a viscous form.
The fluid containment features may also provide a vent gap through which gas can escape from the cavity when the holographic recording material is injected. Furthermore, in addition to providing advantages in the containment of the holographic recording material when the material is in a viscous form, the fluid containment features may also provide an environmental barrier between the holographic recording material and the environment after the holographic recording material is cured.
In another embodiment, the substrates may be formed with centerpieces rather than center holes commonly formed in optical substrates. The centerpieces may serve to more completely encapsulate the cavity, and thereby contain injected holographic recording material within the cavity. Furthermore, the centerpieces may be recessed relative to outer surfaces of the respective substrates.
By recessing the centerpieces relative to outer surfaces of the respective substrates, flatness of the outermost surfaces of the substrates can be improved, allowing the reference planes of a manufacturing device to define improved parallelism between the outer surfaces during the media manufacturing process. In particular, recessed centerpieces may avoid problems caused by thickness variations in proximity to the centerpieces. Therefore, the outer surfaces of the substrates can be forced against reference planes during the media manufacturing process so that the outer surfaces are substantially parallel to one another, without being inhibited by thickness variations in proximity to the centerpieces.
In another embodiment, the invention is directed to a set of substrates for use in a sandwiched construction data storage medium in which a viscous material is sandwiched between a first substrate and a second substrate during fabrication of the medium. The set of substrates may comprise a first substrate including a first fluid containment feature formed in proximity to an outer edge of the first substrate, and a second substrate including a second fluid containment feature formed in proximity to an outer edge of the second substrate.
In another embodiment, the invention may be directed to a holographic data storage system. For example, the system may include a laser that produces at least one laser beam, optical elements through which the laser beam passes, a data encoder that encodes data in at least part of the laser beam, and a holographic recording medium that stores at least one hologram. The holographic recording medium may include a first substrate, a second substrate, and a holographic recording material between the first and second substrates. One or both of the substrates may be formed with one or more of the substrate features described herein.
In another embodiment, the invention may be directed to a method of fabricating a holographic recording medium. For example, the method may include positioning a first substrate relative to a second substrate to define a cavity, the first substrate including a first fluid containment feature formed in proximity to an outer edge of the first substrate, and the second substrate including a second fluid containment feature formed in proximity to an outer edge of the second substrate such that the cavity is defined by inner surfaces of the first and second substrates and at least one of the first and second fluid containment features. The method may further include injecting a viscous holographic recording material into the cavity, and curing the holographic recording material.
The various embodiments may be capable of providing one or more advantages. In particular, the substrate features described herein may improve media quality, simplify and improve the manufacturing process associated with media fabrication, and may provide improved environmental stability to the created media. Additional details of these and other embodiments are set forth in the accompanying drawings and the description below. Other features, objects and advantages will become apparent from the description and drawings and from the claims.
FIG. 1 is a cross-sectional side view of an exemplary holographic data storage medium according to an embodiment of the invention.
FIG. 2 is a top view of the holographic data storage medium illustrated in FIG. 1.
FIG. 3 is a cross-sectional side view illustrating the creation of a holographic medium via a center injection process.
FIG. 4 is a cross-sectional side view of an exemplary top substrate that can be used in a holographic data storage medium.
FIG. 5 is a top view of the top substrate illustrated in FIG. 4.
FIG. 6 is a cross-sectional side view of an exemplary bottom substrate that can be used in a holographic data storage medium.
FIG. 7 is a top view of the top substrate illustrated in FIG. 6.
FIG. 8 is a cross-sectional side view of a set of substrates that can be used in a holographic data storage medium.
FIGS. 9-12 are cross-sectional side views of a portion of a holographic data storage medium during a fabrication process in which a holographic recording material is injected between two substrates.
FIG. 13 is a cross-sectional side view of a portion of a substrate illustrating an injection channel formed in a centerpiece of the substrate.
FIG. 14 is a cross-sectional side view of a portion of a substrate illustrating a runner formed on the centerpiece of the substrate.
FIGS. 15 and 16 are additional cross-sectional side views of an exemplary holographic data storage media according to embodiments of the invention.
FIG. 17 is a block diagram of a holographic data storage system for reading and possibly writing to a holographic recording medium